Abrupt reclosure and gradual restenosis greatly limit the safety and efficacy of percutaneous transluminal balloon angioplasty (BA) in the treatment of obstructive coronary atherosclerosis. Disruption of the arterial wall and lumen geometry may play an important role in the genesis of both complications. Laser balloon angioplasty (LBA), conceived by the Principal Investigator, is a technique, performed immediately after BA, wherein laser- thermal coagulation of soft tissue during the final balloon inflation may be used percutaneously to fuse together disrupted elements of the arterial wall and to reduce elastic recoil, thereby producing a lumen the same size and shape as the cylindrical balloon. Initial results of studies of postmortem human atherosclerotic arteries and of normal canine carotid arteries in vivo indicate that LBA is effective in achieving these effects and that it is well tolerated acutely and chronically. We therefore propose to test the hypothesis that LBA will increase luminal dimensions to a greater extent than BA, acutely and chronically, in patients with symptomatically disabling peripheral arterial insufficiency. Computerized image analysis of angiograms will be used to quantitate luminal dimensions accurately. Prior to this clinical study, additional postmortem studies of human atherosclerotic arteries are proposed to optimize the performance of LBA; thus, for a given balloon size and pattern of Nd:YAG laser radiation within the balloon, the laser power and exposure duration limits for achieving tissue fusion and for markedly reducing elastic recoil over a clinically relevant range of tissue thicknesses and compositions will be defined. In vivo acute and chronic angiographic studies of atherosclerotic rabbit iliac and normal canine coronary arteries subjected to either BA or LBA with one of three laser doses chosen from the in vitro studies will then be used to further refine laser dosimetry for optimal clinical application of LBA. If the hypothesis of the present proposal is proved correct, future studies will be designed to test the hypotheses that LBA can be used to eliminate abrupt reclosure and is associated with a lower incidence of restenosis compared to BA. A marked reduction of the incidence of these complications by successful application of LBA would greatly improve the safety and efficacy of angioplasty, broaden the indications for the procedure, reduce the need for coronary bypass surgery, and reduce the mortality and morbidity from coronary atherosclerosis.